Thousands of passengers were stranded as the metro railway systems in Rio de Janeiro and Sao Paulo shut down. Sao Paulo is home to nearly 20 million people, and Rio to another 15 million.

Tens of thousands of passengers had to walk along the underground tracks to reach stations, where buses provided an emergency service.

To prevent an upsurge in street crime, extra police were put on the streets, and residents in Sao Paulo and Rio were urged not to venture outside their homes.

The power failure was most likely caused by a major fault at the giant Itaipu hydroelectric dam, where a loss of up to 20,000 megawatts was reported after the distribution system was shut down by a storm.